Sputtering target with lowered oxygen content

ABSTRACT

A sputtering target with a lowered oxygen content is provided which can prevent a deterioration in properties of a magnetic film caused by unavoidably included oxygen present in an alloy material system. The sputtering target contains an oxygen scavenger comprising an element capable of reducing metal components constituting the sputtering target, the lowered oxygen content of the sputtering target having been achieved by the oxygen scavenger.

TECHNICAL FIELD

[0001] The present invention relates to a sputtering target for use inthe formation of a thin film by sputtering, and more particularly to asputtering target with a lowered oxygen content.

BACKGROUND ART

[0002] A target material composed of a Co—Cr-base, Co—Ni-base, orCo—Ni—Cr-base alloy has hitherto been industrially used as a sputteringtarget for the formation of a thin film, such as a magnetic film, bysputtering.

[0003] All of the Co—Cr-base, Co—Ni-base, and Co—Ni—Cr-base alloys arerollable, and, thus, a cast ingot produced by melting and casting can berelatively easily rolled to a predetermined thickness.

[0004] In the sputtering targets of alloy systems as described above,oxygen is unavoidably included in the step of the preparation of thestarting material or in the step of the production of the target. Up tonow, attention has not been always fully paid to the presence of oxygenunavoidably included in the alloy system and the regulation of thecontent of oxygen in the alloy system.

[0005] The present inventor has found that, in the above-describedsputtering target materials for the formation of thin films, such asmagnetic films, the properties of the magnetic films, particularlymagnetic properties, are deteriorated by oxygen unavoidably included inthe alloy material system.

DISCLOSURE OF THE INVENTION

[0006] The present invention has been made with a view to solving theabove problems of the prior art, and it is an object of the presentinvention to provide a sputtering target with a significantly loweredcontent of included oxygen causative of a deterioration in theproperties of magnetic films.

[0007] In order to attain the above object of the present invention,there is provided a sputtering target with a lowered oxygen content,said sputtering target containing an oxygen scavenger comprising anelement capable of reducing metal components constituting the sputteringtarget, the lowered oxygen content of the sputtering target having beenachieved by the oxygen scavenger.

[0008] According to a preferred embodiment of the present invention, thecontent of oxygen in the sputtering target is not more than 500 ppm,more preferably not more than 300 ppm, particularly preferably not morethan 10 ppm.

[0009] According to the present invention, the oxygen scavenger ispreferably at least one member selected from the group consisting ofgroup 4A, 3B, and 4B elements, more preferably at least one memberselected from the group consisting of group 4A elements, particularlypreferably at least one member selected from the group consisting oftitanium, aluminum, boron, and carbon, most preferably titanium.

[0010] According to a preferred embodiment of the present invention,melting a starting material for a sputtering target and/or casting themelt involving the addition of the oxygen scavenger is carried out in aCaO crucible. In this case, the oxygen scavenger is most preferablytitanium.

[0011] The sputtering target with a lowered oxygen content according tothe present invention is applicable to an NiFe-base, CoCrPt-base,CoCrPtB-base, CoPt-base, PtMn-base, FeAlSi-base, FeCo-base, or FeMn-basesputtering target.

[0012] According to a preferred embodiment of the present invention, thesputtering target is an NiFe-base, Co-base, or Fe-base target with anoxygen content of not more than 10 ppm, more preferably not more than 5ppm.

[0013] According to a preferred embodiment of the present invention, theconcentration of the residual oxygen scavenger in the sputtering targetis not more than 200 ppm, preferably not more than 100 ppm, morepreferably not more than 50 ppm.

BEST MODE FOR CARRYING OUT THE INVENTION

[0014] The sputtering target with a lowered oxygen content according tothe present invention contains an oxygen scavenger comprising an elementcapable of reducing metal components constituting the sputtering target,the lowered oxygen content of the sputtering target having been achievedby the oxygen scavenger.

[0015] In the sputtering target with a lowered oxygen content accordingto a preferred embodiment of the present invention, the content ofoxygen in the sputtering target is not more than 500 ppm, morepreferably not more than 300 ppm, particularly preferably not more than10 ppm.

[0016] The oxygen scavenger according to the present invention ispreferably at least one member selected from the group consisting ofgroup 4A, 3B, and 4B elements, more preferably at least one memberselected from the group consisting of group 4A elements, particularlypreferably at least one member selected from the group consisting oftitanium, aluminum, boron, and carbon.

[0017] The sputtering target with a lowered oxygen content according tothe present invention is applicable to an NiFe-base, CoCrPt-base,CoCrPtB-base, CoPt-base, PtMn-base, FeAlSi-base, FeCo-base, or FeMn-basesputtering target.

[0018] According to a preferred embodiment of the present invention, thesputtering target is an NiFe-base, Co-base, or Fe-base target with anoxygen content of not more than 10 ppm, more preferably not more than 5ppm.

[0019] According to a preferred embodiment of the present invention, theconcentration of the residual oxygen scavenger in the sputtering targetis not more than 200 ppm, preferably not more than 100 ppm, morepreferably not more than 50 ppm.

[0020] The present invention will be described in more detail withreference to the production process of the present invention.

[0021] In the production process according to the present invention, invacuo, constituent metal materials for constituting a sputtering targetare melted, and the melt is then cast. The melting-casting process perse may be carried out by a conventional process. After casting, the castingot thus obtained is optionally rolled, followed by machining (forexample, cutting) to provide a predetermined sputtering target.

[0022] The sputtering target with a lowered oxygen content according tothe present invention is applicable to an NiFe-base, CoCrPt-base,CoCrPtB-base, CoPt-base, PtMn-base, FeAlSi-base, FeCo-base, or FeMn-basesputtering target. According to a preferred embodiment of the presentinvention, the sputtering target is an NiFe-base, Co-base, or Fe-basetarget.

[0023] Preferred production processes will be described for each type ofthe alloy system.

[0024] In the case of an NiFe-base alloy system, the step of melting andcasting is carried out, for example, under a vacuum of not more than3×10⁻⁴ Torr. The resultant cast ingot is rolled at a temperature ofabout 1,100° C. to provide a rolled plate which is then cut to a productsize, followed by machining such as lathing or milling. Thus, asputtering target is produced.

[0025] In the case of a CoCrPt-base alloy system, the step of meltingand casting is carried out, for example, under a vacuum of not more than3×10⁻² Torr. The resultant cast ingot is rolled at a temperature ofabout 1,100 to 1,200° C. to provide a rolled plate which is then cut toa product size, followed by machining such as lathing or milling. Thus,a sputtering target is produced.

[0026] In the case of a PtMn-base alloy system, the step of melting andcasting is carried out, for example, under a vacuum of not more than3×10⁻² Torr. The resultant cast ingot is subjected to machining, such aslathing or milling, to produce a sputtering target. This sputteringtarget is generally joined to a predetermined backing plate.

[0027] In the sputtering target according to the present invention, anoxygen scavenger comprising an element capable of reducing metalcomponents for constituting the sputtering target is added in the stepof melting and casting. A lowering in oxygen content has been achievedby this oxygen scavenger.

[0028] The oxygen scavenger added is preferably at least one memberselected from the group consisting of group 4A, 3B, and 4B elements,more preferably at least one member selected from the group consistingof group 4A elements, particularly preferably at least one memberselected from the group consisting of titanium, aluminum, boron, andcarbon. According to the present invention, the oxygen scavenger is mostpreferably titanium.

[0029] According to the present invention, in the step of melting andcasting, in particular, when the base metal in the melting is iron, itis considered that the presence of an oxygen scavenger, for example,titanium, permits the following reaction to proceed in the molten metal:2/3Fe₂O₃+Ti=TiO₂+4/3Fe. TiO₂ floats, on the surface of a molten metal,as dross (a scum component of oxides) which, therefore, can beeffectively removed.

[0030] The present inventor has found that the oxygen content can befurther lowered by carrying out the step of melting (dissolution) and/orcasting in a CaO crucible. The present inventor has further found thatthe use of a combination of the CaO crucible with titanium among theabove-described oxygen scavengers can offer improved oxygen scavengingeffect surpassing the expected effect, and, at the same time, can offerdesulfurization effect. The development of this advantageous cooperativefunction and effect attained by the above combination is particularlysignificant in a PtMn-base sputtering target. It has hitherto beenrelatively difficult to scavenge oxygen from the PtMn-base sputteringtarget.

[0031] The reason why the above advantageous cooperative function andeffect can be developed has not been fully elucidated yet. However, thereason is believed to be as follows, although the present invention isnot limited to any theory. Specifically, TiO₂ as a deoxidation productin the molten metal is absorbed in the CaO crucible according to thefollowing reaction formula:

CaO+TiO₂=CaO.TiO₂

[0032] At that time, on the wall surface of the crucible, CaOeffectively functions to simultaneously cause a desulfurization reactionaccording to the following reaction formula:

Ti+2CaO+2S =2CaS+TiO₂

[0033] The amount of the oxygen scavenger added in the step of meltingand casting is properly selected according to the estimated content ofdissolved oxygen. In general, however, the amount of the oxygenscavenger added is suitably in the range of 0.001 to 1.0% by weight,preferably in the range of 0.001 to 0.5% by weight, more preferably inthe range of 0.001 to 0.5% by weight.

[0034] In particular, in the PtMn-base sputtering target, in meltingplatinum and manganese in the CaO crucible, the addition of titaniumpreferably in an amount of 0.001 to 3% by weight, more preferably 0.01to 0.5% by weight, based on the amount of manganese can lower the oxygencontent, for example, to not more than 50 ppm. Further, in this case,the amount of residual titanium can be reduced to not more than 200 ppm.

[0035] According to the present invention, the addition of the oxygenscavenger in the above amount range permits the content of oxygen in thesputtering target to be regulated to not more than 500 ppm, morepreferably not more than 300 ppm, particularly preferably not more than10 ppm. Further, in particular, in the case of an NiFe-base, Co-base, orFe-base sputtering target, the oxygen content can be regulated to notmore than 10 ppm, more preferably not more than 5 ppm.

[0036] According to the present invention, the concentration of theresidual oxygen scavenger in the sputtering target after the removal ofoxygen is not more than 200 ppm, preferably not more than 100 ppm, morepreferably not more than 50 ppm. The present inventor has found that aconcentration of the residual oxygen scavenger of not more than 100 ppmdoes not adversely affect the properties of the sputtering target.

EXAMPLES

[0037] The following examples further illustrate the present invention,but should not be construed as limiting the present invention.

Example 1 Production of NiFe-base Sputtering Target with Lowered OxygenContent

[0038] A mass of nickel (5,000.0 g, 20×20×5 mm, 3N5), a mass of iron(1,110.0 g, 15×15×5 mm, 3N5), and a piece of titanium (1.8 g, 5×5×1 mm,4N) (total weight 6,111.8 g; amount of titanium added 0.05% by weight)were placed in an MgO crucible, and were then melted in a vacuum meltingfurnace by high frequency melting.

[0039] The melting temperature was up to 1450° C., and the system wasevacuated to not more than 3×10⁻⁴ Torr. About two hr after theinitiation of melting, the melt was cast in a mold which had beenpreviously provided (casting temperature 1360° C.) to prepare an ingothaving a size of 150×150×20 t.

[0040] This ingot was heated at 1100° C. for one hr, and then rolled.The rolling was carried out by four passes for one heating, and this wasrepeated several times to prepare a rolled plate having a predeterminedthickness (5 to 7 mm).

[0041] A sample having a size of about 5 mm square was taken off fromthe rolled plate by wire cutting, and applied to gas analysis(non-dispersive infrared absorption analysis with dissolution in inertgas).

[0042] As a result, for a sample on melting without the addition oftitanium, the oxygen content was 35 ppm, whereas, for the sample onmelting with the addition of titanium, the oxygen content was 2.8 ppm.The amount of titanium remaining in the sample was 60 ppm.

Example 2 Production of PtMn-base Sputtering Target

[0043] A piece of platinum (7,282.0 g, 40×20×1 mm, 3N5), a mass ofmanganese (2,718.0 g, 15×15×5 mm, 3N), and a piece of titanium (5.0 g,5×5×1 mm, 3N5) (total weight 10,005.0 g; amount of titanium added 0.05%by weight) were placed in an MgO crucible, and were then melted in avacuum melting furnace by high frequency melting.

[0044] After the evacuation of the furnace, the furnace was filled withargon gas, and raising the temperature was initiated. The furnace wasthen evacuated in argon atmosphere to not more than 3×10⁻² Torr. Abouttwo hr after the initiation of melting, the melt was cast in a moldwhich had been previously provided (casting temperature 1430° C.) toprepare an ingot having a size of 150 ø×20 t.

[0045] A sample having a size of about 5 mm square was taken off fromthe ingot by wire cutting, and applied to gas analysis (non-dispersiveinfrared absorption analysis with dissolution in inert gas).

[0046] As a result, for a sample on melting without the addition oftitanium, the oxygen content was 900 ppm, whereas, for the sample onmelting with the addition of titanium, the oxygen content was 250 ppm.The amount of titanium remaining in the sample was 70 ppm.

Example 3 Production of CoCrPtTa-base Sputtering Target

[0047] A mass of cobalt (866.4 g, 20×20×5 mm, 3N5), a mass of chromium(186.6 g, 30×30×8 mm, 3N5), a piece of platinum (235.8 g, 40×20×1 mm,3N5), tantalum particles (109.2 g, 5×7×6 mm, 3N5), and a piece oftitanium (0.7 g, 5×5×1 mm, 3N5) (total weight 1,398.7 g; amount oftitanium added 0.05% by weight) were placed in an MgO crucible, and werethen melted in a vacuum melting furnace by high frequency melting.

[0048] The melting temperature was up to 1450° C., and the system wasevacuated to not more than 3×10⁻⁴ Torr. About two hr after theinitiation of melting, the melt was cast in a mold which had beenpreviously provided (casting temperature 1360° C.) to prepare an ingothaving a size of 100×150×15 t.

[0049] This ingot was heated at 1100° C. for one hr, and then rolled.The rolling was carried out by two passes for one heating, and this wasrepeated several times to prepare a rolled plate having a predeterminedthickness (5 to 7 mm).

[0050] A sample having a size of about 5 mm square was taken off fromthe rolled plate by wire cutting, and applied to gas analysis(non-dispersive infrared absorption analysis with dissolution in inertgas).

[0051] As a result, for a sample on melting without the addition oftitanium, the oxygen content was 35 ppm, whereas, for the sample onmelting with the addition of titanium, the oxygen content was 9 ppm. Theamount of titanium remaining in the sample was 70 ppm.

Example 4

[0052] Sputtering targets were produced in the same manner as inExamples 1 to 3, except that a CaO crucible was used instead of the MgOcrucible.

[0053] For the sputtering targets thus obtained, the oxygen content wasas follows, and, for all the targets, the results were satisfactorilygood.

[0054] NiFe-base target: oxygen content 3 ppm

[0055] PtMn-base target: oxygen content 40 ppm

[0056] CoCrPtTa-base target: oxygen content 5 ppm

[0057] As is apparent also from the results of the examples, thesputtering target according to the present invention contains an oxygenscavenger comprising an element capable of reducing metal componentsconstituting the sputtering target, the lowered oxygen content of thesputtering target having been achieved by the oxygen scavenger. Thus,the present invention can provide a sputtering target with a loweredoxygen content which can prevent a deterioration in properties ofmagnetic films caused by unavoidably included oxygen present in an alloymaterial system, and, hence, is very useful from the viewpoint ofindustry.

What is claimed is:
 1. A sputtering target with a lowered oxygencontent, said sputtering target containing an oxygen scavengercomprising an element capable of reducing metal components constitutingthe sputtering target, the lowered oxygen content of the sputteringtarget having been achieved by the oxygen scavenger.
 2. The sputteringtarget with a lowered oxygen content according to claim 1, which has anoxygen content of not more than 500 ppm, preferably not more than 300ppm, more preferably not more than 200 ppm, still more preferably notmore than 50 ppm, still more preferably not more than 10 ppm.
 3. Thesputtering target with a lowered oxygen content according to claim 1,wherein the oxygen scavenger is at least one member selected from thegroup consisting of group 4A, 3B, and 4B elements.
 4. The sputteringtarget with a lowered oxygen content according to claim 1, whereinmelting a starting material for a sputtering target and/or casting themelt involving the addition of the oxygen scavenger is carried out in aCaO crucible.
 5. The sputtering target with a lowered oxygen contentaccording to claim 1, wherein the oxygen scavenger is at least onemember selected from the group consisting of group 4A elements.
 6. Thesputtering target with a lowered oxygen content according to claim 1,wherein the oxygen scavenger is at least one member selected from thegroup consisting of titanium, aluminum, boron, and carbon.
 7. Thesputtering target with a lowered oxygen content according to claim 1,wherein the oxygen scavenger is titanium.
 8. The sputtering target witha lowered oxygen content according to claim 1, wherein the sputteringtarget is an NiFe-base, CoCrPt-base, CoCrPtB-base, CoPt-base, PtMn-base,FeAlSi-base, FeCo-base, or FeMn-base target.
 9. The sputtering targetwith a lowered oxygen content according to claim 1, wherein thesputtering target is an NiFe-base, Co-base, or Fe-base target with anoxygen content of not more than 10 ppm, preferably not more than 5 ppm.10. The sputtering target with a lowered oxygen content according toclaim 1, wherein the concentration of the residual oxygen scavenger inthe sputtering target is not more than 200 ppm, preferably not more than100 ppm, more preferably not more than 50 ppm.